Various methods for incorporating biocides into resin compositions have been disclosed in the prior art. By way of illustration, U.S. Pat. No. 4,086,297 discloses a process for forming a solid thermoplastic composition containing a microbiocide utilizing very high levels of the microbiocide and two thermoplastic resins in conjunction with melt blending processing.
As another illustration, U.S. Pat. No. 4,663,359 discloses a process for preparing a microbiocide concentrate which is useful in plastisol systems. The process comprises mixing a porous thermoplastic resin powder with a high concentration of microbiocide at an elevated temperature sufficient to melt the biocide and open the pores of the resin, and incorporating the melted biocide into the pores of the porous resin, optionally in the presence of a carrier. The resulting product is provided as a dry, free-flowing powder containing the microbiocide in a high concentration at least about 20 times greater than the normal upper usage concentration for the microbiocide.
Unfortunately, the products produced in accordance with the above-mentioned '297 and '395 patents are solids which are frequently more difficult to process into a finished product than might be desired. Liquid dispersions would avoid such solids handling problems in subsequent processing steps. Heretofore, however, suitable methods for incorporating insoluble or difficult-to-solubilize additives, such as biocides, into liquid dispersions has represented a challenge to the plastics manufacturing community. The solids in such liquid dispersions tend to settle out over time, thus causing a non-uniform distribution of the additive in the dispersion. In addition, certain liquid dispersions, most notably plastisols, tend to increase in viscosity with increasing temperature, thus posing a risk that the dispersion will "set-up" or solidify during storage and/or handling prior to use.
In view of the above, new methods for incorporating insoluble or difficult-to-solubilize biocides into plastics resins that avoid the settling and/or viscosity increase problems of the prior art compositions would be highly desired by the plastics manufacturing community.